Traffic Forwarding

ABSTRACT

The present disclosure describes traffic forwarding in a network where a virtual local area network (VLAN) exists in multiple network sites that are geographically dispersed and connected via virtual links. A first edge device (ED) at a first site receives, from a second ED at a second site, information identifying a VLAN of the second ED through a virtual link. The VLAN identified in the information is an active VLAN of the second ED. An association between (i) the VLAN of the second ED and (ii) the virtual link through which the information is received from the second ED is recorded. When forwarding traffic to the VLAN of the second ED, it is determined the virtual link associated with the VLAN of the second ED is determined based on the recorded association and the traffic is forwarded via the determined virtual link.

BACKGROUND

To provide better services, network providers often deploy multiple data centres in different physical locations for load sharing and improved reliability. For example, virtual machine migration allows data centres to share workloads across physical machines. Since the process of virtual machine migration is transparent to users, the virtual machine generally retains its Internet Protocol (IP) address. Connecting geographically dispersed data centres at various network sites at Layer 2 facilitates such virtual machine migration.

BRIEF DESCRIPTION OF DRAWINGS

By way of examples, the present disclosure will be described with reference to the following drawings, in which:

FIG. 1 is a schematic diagram of an example network for traffic forwarding, indicating flows of information identifying active virtual local area networks (VLANs);

FIG. 2 is a flowchart of an example method for traffic forwarding;

FIG. 3 is a schematic diagram of the example network environment in FIG. 1, indicating flows of traffic;

FIG. 4 is a block diagram of a first example structure of a network device capable of acting as an edge device; and

DETAILED DESCRIPTION

In a network connecting multiple geographically dispersed network sites, traffic for a VLAN is forwarded by a first edge device (ED) at a first site to a second ED at a second site regardless of whether the VLAN is an active VLAN of the second ED (i.e. whether the second ED is responsible for forwarding traffic within the VLAN at the second site). If the second ED receives traffic for a VLAN that is not its active VLAN, it will simply discard the traffic. This wastes the processing resources of the first ED for sending unnecessary traffic, and of the second ED for receiving and processing unnecessary traffic.

The present disclosure describes traffic forwarding in a network where a VLAN exists in multiple network sites that are geographically dispersed and connected via virtual links. A first edge device (ED) at a first site receives, from a second ED at a second site, information identifying a VLAN of the second ED through a virtual link. The VLAN identified in the information is an active VLAN of the second ED. An association between (i) the VLAN of the second ED and (ii) the virtual link through which the information is received from the second ED is recorded. When forwarding traffic of the VLAN of the second ED, the virtual link associated with the VLAN of the second ED is determined based on the recorded association, and the traffic is forwarded via the determined virtual link.

According to the present disclosure, the first ED forwards traffic of a particular VLAN to a second ED only if the VLAN is an active VLAN of the second ED (i.e. the second ED is responsible for forwarding traffic within the VLAN at the second site). Since the second ED notifies the first ED of its active VLAN, it is known to the first ED whether a particular VLAN is an active VLAN of the second ED, and the associated virtual link through which the traffic is forwarded.

The present disclosure improves over the case where traffic for a VLAN is simply forwarded by the first ED to the second ED a regardless of whether the VLAN is an active VLAN of the second ED. For example, since traffic forwarding is based on the recorded association in the present disclosure, this relieves the first ED from sending unnecessary traffic (i.e. traffic for a VLAN that is not its active VLAN) to the second ED, and the second ED from receiving and processing the unnecessary traffic. Also, since the traffic is generally forwarded from the first ED to the second ED through a core network (e.g. public network), this also reduces the traffic burden on the network.

Examples will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an example network 100 where a VLAN exists in multiple network sites 110 that are geographically dispersed and connected via virtual links 122. The term “virtual link” in the present disclosure refers broadly to any communication channel suitable for connecting the geographically dispersed network sites over a Layer 3 network. In one example, a physical communication medium may be virtualized to include multiple communication channels such that traffic of one communication channel is separated from that of a different communication channel (e.g. using a suitable identifier). The virtual link may be a Layer 2 virtual link (e.g. virtual Ethernet link) tunnelled through the Layer 3 network using any suitable protocol. The example network 100 may be any suitable network, such as Ethernet Virtual Interconnect (EVI) and Overlay Transport Virtualization (OTV) etc.

There are three sites 110 in the example: Site 1, Site 2 and Site 3. Each site is deployed with a data centre which is connected to a Layer 3 public network 120 (i.e. core network) at Layer 2 via at least one ED 112. For example, Site 1 is deployed with ED1, Site 2 with ED2 and Site 3 with Device A and Device B. The EDs perform functions relating to traffic access within a virtual private network (VPN), including traffic forwarding to and from the public network 120. The EDs may be any suitable network devices, such as routers, switches etc.

In the network 100, VLAN1 to VLAN20 exist in all three network sites 110, and traffic is forwarded between EDs 112 via virtual links 122 connecting the EDs 112. A virtual link 122 will also be referred to as a “virtual layer-2 link”, “virtual Ethernet link” or “vlink” in the present disclosure. For example in FIG. 1, ED1 is connected to Device B via ‘vlink1’, Device A via ‘vlink2’, and ED2 via ‘vlink3’. Using an EVI network as an example, each virtual link represents a bidirectional virtual Ethernet connection between two EVI instances. Multiple virtual links are supported by an EVI tunnel to support transparent forwarding between different EDs. EVI instances, which are virtual interconnect instances, are uniquely identified by a Network ID and set up such that traffic forwarding in different EVI instances is isolated from each other.

Two types of sites are shown in FIG. 1: multi-homed and single-homed.

-   -   A multi-homed site interfaces with the public network 120 via         multiple EDs. For example, Site 3 is a multi-homed site in which         Device A and Device B both connect Site 3 to the public network         120. Incoming and outgoing traffic to and from the public         network 120 is forwarded via Device A and/or Device B.     -   On the other hand, in a single-homed site, only one ED 112         serves as an incoming and outgoing interface to the public         network 120. For example, Site 1 and Site 2 are connected to the         public network 120 via ED1 and ED2 respectively.

When broadcasting traffic or flooding multicast traffic within the EVI network 100, the traffic is forwarded to the EDs 112 via the public network 120. For a multi-homed site with multiple EDs 112, one ED 112 is elected as the AED (Authentication ED or Authoritative ED) for a particular VLAN. When traffic for a particular VLAN is received by the AED of the VLAN, the traffic will be forwarded within the VLAN. The VLAN for which the AED is responsible as the traffic forwarder is referred to as an “active VLAN” of the AED.

A non-AED for a VLAN, however, is not responsible for traffic forwarding within that VLAN and will simply discard the received traffic. For example in FIG. 1:

-   -   ED1 at single-homed Site 1 is the AED of VLAN1 to VLAN20, which         are active VLANs of ED1.     -   ED2 at single-homed Site 2 is the AED of VLAN1 to VLAN20, which         are active VLANs of ED2.     -   Device A at multi-homed Site 3 is the AED of VLAN1 to VLAN10,         which are active VLANs of Device A. Device A is a non-AED for         VLAN11 to VLAN20, and will discard any received traffic for         VLAN11 to VLAN20.     -   Device B at multi-homed Site 3 is the AED of VLAN11 to VLAN20,         which are also active VLANs of Device B. Device B a non-AED for         VLAN1 to VLAN10, and will discard any received traffic for VLAN1         to VLAN10.

FIG. 2 is a flowchart of an example method 200 for traffic forwarding in the network 100 in FIG. 1. The method 200 may be applied in a first ED 112 at a first site 100 in FIG. 1.

-   -   At block 210, the first ED receives, from a second ED at a         second site, information identifying a VLAN of the second ED.         The VLAN is an active VLAN of the second ED, i.e. the second ED         is responsible for forwarding traffic within the VLAN at the         second site.     -   At block 220, the first ED records an association (e.g.         corresponding relationship) between (i) the VLAN identified in         the received information and (ii) a virtual link through which         the information is received.     -   At block 230, when forwarding traffic to the VLAN, the first ED         determines a virtual link corresponding to the VLAN based on the         recorded association, and forwards the traffic to the VLAN via         the determined virtual link. The traffic may be broadcasted in         the case of broadcast traffic or flooded in the case of         multicast traffic.

If the first ED has any active VLAN, the first ED also sends information identifying its active VLAN or VLANs via virtual links of the first ED similar to block 210.

Various examples will now be described using FIG. 1 and FIG. 3. The arrows in FIG. 1 (i.e. 132, 134, 136, 142, 144, and 146) indicate the flows of information identifying active VLANs according to block 210. In FIG. 3 however, the arrows (i.e. 312, 314, 322, and 324) indicate the flows of traffic among the EDs 112.

Using ED1 in FIG. 1 and FIG. 3 as a first example:

-   -   ED1 sends information identifying its active VLANs (i.e.         VLAN1-VLAN10) via its virtual links. That is, via vlink1 to         Device B (see 132 in FIG. 1), vlink2 to Device A (see 134), and         vlink3 to ED2 (see 136).     -   ED1 also receives information identifying active VLANs of other         EDs (i.e. Device B, Device A and ED2) at other sites. That is,         VLAN1-10 from Device A via vlink2 (see 142 in FIG. 1), VLAN11-20         from Device B via vlink1 (see 144) and VLAN1-20 from ED2 via         vlink3 (see 146).     -   ED1 records the following associations (see also 310 in FIG. 3):         -   Record 1: VLAN1 to VLAN10, vlink2, vlink3.         -   Record 2: VLAN11 to VLAN20, vlink1, vlink3.     -   When forwarding traffic to VLAN1, ED1 searches Record 1 and         Record 2 to determine the virtual links associated with VLAN1,         i.e. vlink2 and vlink3 in Record 1. ED1 then forwards the         traffic for VLAN1 via vlink2 to Device A (see 312 in FIG. 3) and         via vlink3 to ED2 (see 314 in FIG. 3).

As such, in the above example, ED1 does not forward traffic for VLAN1 to Device B because vlink1 connecting ED1 and Device B is not associated with VLAN1 in Record 1 (see 310 in FIG. 3). In particular, since VLAN1 is not an active VLAN of Device B, ED1 never receives information from Device B that identifies VLAN1 as its active VLAN. This relives the public network 120 from unnecessary traffic, and Device B from processing traffic for which it is not an AED. Also, ED1 does not have to waste resources replicating the traffic and sending it to Device B.

Similarly, using ED2 in FIG. 1 and FIG. 3 as a second example:

-   -   ED2 records the following associations based on information         identifying active VLANs from ED1, Device A and Device B (see         320 in FIG. 3):         -   Record 1: VLAN1 to VLAN10, vlink3, vlink4.         -   Record 2: VLAN11 to VLAN20, vlink3, vlink5.     -   When forwarding traffic to VLAN11, ED2 searches Record 1 and         Record 2 to determine the virtual links associated with VLAN11,         i.e. vlink3 and vlink5 in Record 2. ED2 then forwards the         traffic via vlink5 to Device B (see 322 in FIG. 3) and via         vlink3 to ED1 (see 324 in FIG. 3).

Again, ED2 does not forward traffic for VLAN11 to Device A because vlink4 connecting ED2 and Device A is not associated with VLAN11 in Record 2 (see 320 in FIG. 3). In particular, since VLAN11 is not an active VLAN of Device A, ED2 never receives information from Device A that identifies VLAN11 as its active VLAN. Again, this relives the public network 120 from unnecessary traffic, and Device A from processing traffic for which it is not an AED. Also, ED2 does not have to waste processing resources for replicating the traffic to VLAN11 and sending it to Device A.

The above associations may be stored as database items in a database accessible by the ED, either locally created at an ED or a remote database. The database may be a database storing public network forwarding information etc.

In the above examples, the information identifying active VLANs may be sent using any suitable protocol, including Intermediate-System-to-Intermediate System (ISIS) protocol notification etc. In this case, the information may be included in link state packets sent using IS-IS.

In the case of a multi-homed site (e.g. Site 3 with Device A and Device B), all EDs 112 at the site 110 are configured with the same VLANs but not all of them are responsible for traffic forwarding for all VLANs. For example, the EDs may undergo a negotiation or election process to elect an ED that is responsible for traffic forwarding within particular VLAN(s).

Any suitable election process may be used. For example, in FIG. 1 and FIG. 3, VLANs 1-20 are divided equally among the Device A and Device B. Device A and Device B negotiate among themselves to select their Active VLANs, i.e. Device A is elected to be responsible for its VLAN1 to VLAN10, and Device B for VLAN11 to VLAN20. Alternatively, the VLANs may be randomly assigned to the EDs or depending of any suitable criteria such as load etc.

In the case of a single-home site, no election process is required. Since there is only one ED, the active VLANs of the ED are VLANs used for layer 2 virtual interconnect, which are also known as extended VLANs of the ED.

Edge Device 112

The above examples can be implemented by hardware, software or firmware or a combination thereof. Referring to FIG. 4, an example network device 400 capable of acting as an

ED 112 in a network 100 where exists in multiple network sites that are geographically dispersed and connected via virtual links such as the example in FIG. 1 is shown.

The example network device 400 includes a processor 410, a memory 420 and a network interface device 440 that communicate with each other via bus 430. The memory 420 stores any necessary data 422 and machine-readable instructions 424 to perform any of the processes described in the present disclosure. In one example, the data 422 may include an association between (i) a VLAN of a second ED and (ii) a virtual link through which information identifying (i) is received from the second ED.

The processor 410 is further to perform processes described herein. In one example, the network device 400 is capable of acting as a first ED at a first site in the network, and the processor 410 is to:

-   -   Receive, from a second ED at a second site, information         identifying a VLAN of the second ED through a virtual link. The         VLAN identified in the information is an active VLAN of the         second ED.     -   Record an association between (i) the VLAN of the second ED         and (ii) the virtual link through which the information is         received from the second ED.     -   When forwarding traffic to the VLAN of the second ED, determine         the virtual link associated with the VLAN of the second ED based         on the recorded association and forward the traffic via the         determined virtual link.

The memory 420 may store machine-readable instructions 424 to cause the processor 410 to perform processes described herein. In one example, the instructions 424 may include:

-   -   Receiving instructions to cause the processor 410 to receive,         from a second ED at a second site, information identifying a         VLAN of the second ED through a virtual link, wherein the VLAN         identified in the information is an active VLAN of the second         ED.     -   Recording instructions to cause the processor 410 to record an         association between (i) the VLAN of the second ED and (ii) the         virtual link through which the information is received from the         second ED.     -   Forwarding instructions to cause the processor 410 to, when         forwarding traffic to the VLAN of the second ED, determine the         virtual link associated with the VLAN of the second ED based on         the recorded association and forward the traffic via the         determined virtual link.

The network device 400 in FIG. 4 may include units to perform the processes described herein. In one example, the network device 400 may include the following units:

-   -   Receiving unit to receive, from a second ED at a second site,         information identifying a VLAN of the second ED through a         virtual link. The VLAN identified in the information is an         active VLAN of the second ED.     -   Recording unit to record an association between (i) the VLAN of         the second ED and (ii) the virtual link through which the         information is received from the second ED.     -   Forwarding unit to, when forwarding traffic to the VLAN of the         second ED, determine the virtual link associated with the VLAN         of the second ED based on the recorded association and forward         the traffic via the determined virtual link.

The methods, processes and functional units described herein may be implemented by hardware (including hardware logic circuitry), software or firmware or a combination thereof.

The term ‘processor’ is to be interpreted broadly to include a processing unit, ASIC, logic unit, or programmable gate array etc. The processes, methods and functional units may all be performed by the one or more processors 410; reference in this disclosure or the claims to a ‘processor’ should thus be interpreted to mean ‘one or more processors’.

Although one network interface device 440 is shown in FIG. 4, processes performed by the network interface device 440 may be split among multiple network interface devices (not shown for simplicity). As such, reference in this disclosure to a ‘network interface device’ should be interpreted to mean ‘one or more network interface devices”.

Further, the processes, methods and functional units described in this disclosure may be implemented in the form of a computer software product. The computer software product is stored in a storage medium and comprises a plurality of instructions for making a processor to implement the methods recited in the examples of the present disclosure.

The figures are only illustrations of an example, wherein the units or procedure shown in the figures are not necessarily essential for implementing the present disclosure. Those skilled in the art will understand that the units in the device in the example can be arranged in the device in the examples as described, or can be alternatively located in one or more devices different from that in the examples. The units in the examples described can be combined into one module or further divided into a plurality of sub-units.

Although the flowcharts described show a specific order of execution, the order of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be changed relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the present disclosure.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 

1. A method for traffic forwarding in a network where a virtual local area network (VLAN) exists in multiple network sites that are geographically dispersed and connected via virtual links, the method being applicable to a first edge device (ED) at a first site, the method comprising: receiving, from a second ED at a second site, information identifying a VLAN of the second ED through a virtual link, wherein the VLAN identified in the information is an active VLAN of the second ED; recording an association between (i) the VLAN of the second ED and (ii) the virtual link through which the information is received from the second ED; and when forwarding traffic to the VLAN of the second ED, determining the virtual link associated with the VLAN of the second ED based on the recorded association and forwarding the traffic via the determined virtual link.
 2. The method of claim 1, further comprising sending information identifying a VLAN of the first ED via a virtual link of the first ED, wherein the VLAN identified in the information is an active VLAN of the first ED.
 3. The method of claim 2, wherein the first site is a multi-homed site that connects to a public network via the first ED and at least one other ED, and the method further comprises: negotiating with the at least one other ED to elect the first ED as being responsible for traffic forwarding within the active VLAN of the first ED.
 4. The method of claim 2, wherein the first site is a single-homed site that connects to a public network via the first ED only, and the method further comprises: setting a VLAN used for layer 2 virtual interconnection as the active VLAN of the first ED.
 5. The method of claim 1, wherein the information identifying the VLAN of the second ED is received using Intermediate System-to-Intermediate System (ISIS) Protocol notification
 6. The method of claim 1, wherein: the association between the VLAN of the second ED and the virtual link through which the information identifying the active VLAN of the second ED is recorded in a database item in a database; and determining the virtual link associated with the VLAN of the second ED comprises searching for a database item containing the VLAN in the database.
 7. The method of claim 1, wherein the traffic is a broadcast traffic for broadcasting or multicast traffic for flooding.
 8. The method of claim 1, wherein the network connecting multiple network sites at layer 2 is Ethernet Virtual Interconnect (EVI), and the virtual link is a virtual Ethernet link.
 9. A network device for traffic forwarding in a network where a virtual local area network (VLAN) exists in multiple network sites that are geographically dispersed and connected via virtual links, wherein the network device is capable of acting as a first edge device (ED) at a first site, and comprises a processor to: receiving, from a second ED at a second site, information identifying a VLAN of the second ED through a virtual link, wherein the VLAN identified in the information is an active VLAN of the second ED; recording an association between (i) the VLAN of the second ED and (ii) the virtual link through which the information is received from the second ED; and when forwarding traffic to the VLAN of the second ED, determining the virtual link associated with the VLAN of the second ED based on the recorded association and forwarding the traffic via the determined virtual link.
 10. The network device of claim 9, wherein the processor is further to send information identifying a VLAN of the first ED via a virtual link of the first ED, wherein the VLAN identified in the information is an active VLAN of the first ED.
 11. The network device of claim 10, wherein the first site is a multi-homed site that connects to a public network via the first ED and at least one other ED, and the processor is further to: negotiate with the at least one other ED to elect the first ED as being responsible for traffic forwarding within the active VLAN of the first ED.
 12. The network device of claim 10, wherein the first site is a single-homed site that connects to a public network via the first ED only, and the processor is further to: set a VLAN used for layer 2 virtual interconnection as the active VLAN of the first ED.
 13. The network device of claim 9, wherein the information identifying the VLAN of the second ED is received using Intermediate System-to-Intermediate System (ISIS) Protocol notification
 14. The network device of claim 9, wherein the traffic is a broadcast traffic for broadcasting or multicast traffic for flooding.
 15. The network device of claim 9, wherein the network connecting multiple network sites at layer 2 is Ethernet Virtual Interconnect (EVI), and the virtual link is a virtual Ethernet link. 